A sealing device is provided on a portion of a cylinder head of an engine where an injector is attached to in order to prevent high-pressure combustion gas from leaking through an annular gap between an attachment hole formed in the cylinder head and the injector. Moreover, a sealing device is similarly provided on a portion of the cylinder head where sensors and so forth are attached to. In such a sealing device, a technique that employs a resinous sealing ring that has a smaller number of components and can better suppress noise from vibration, when compared with the case of using a metal washer-like sealing, is known.
However, the resinous sealing ring has a problem that a compressing margin on an outer peripheral side decreases with time due to creep deformation and hence its sealing performance eventually deteriorates. In order to solve such a problem, techniques that employ a structure in which a self-sealing function is exerted due to the pressure of combustion gas or a structure in which a surface pressure is partially increased are known (see Patent Literatures 1, 2, and 3). Although such techniques can extend the life span to some degree, it cannot be said that those techniques can sufficiently suppress deterioration of the sealing performance due to a continuing decrease in the compression margin. In particular, countermeasures against the deterioration of the sealing performance due to a loss of compression margin and in low-temperature, low-pressure condition are not sufficient.
Moreover, a technique of suppressing deterioration of the sealing performance by providing an elastic member on an inner peripheral side of a resinous sealing ring that presses the sealing ring toward an outer peripheral side is also known (see Patent Literature 4). However, in this technique, the elastic member is directly exposed to combustion gas. It is, therefore, required to use a material having high heat resistance for the elastic member, and there is another problem that the function of the elastic member deteriorates. Accordingly, there is still room for improvement.